1. Field of the Invention
The present invention relates to a process for displaying the mean modulation error ratio MERRmS of an orthogonal frequency division and multiplexing (OFDM) multicarrier signal.
2. Description of the Background Art
The modulation error ratio (MER) is an important characteristic value for the OFDM (Orthogonal Frequency Division and Multiplexing)—Multicarrier Systems used in modern transmission technology, for example in DAB (Digital Audio Broadcasting) or DVB-T (Digital Video Broadcasting-Terrestrial), as it indicates the mean and maximum deviation of the amplitude and phase statuses (I and Q values) used in this case from the ideal signal statuses of the digital modulation used and therefore provides a measure for the signal quality. The modulation error ratio is given as a mean value and as a maximum value. In order to calculate it all decision fields of the modulation vector diagram are examined in succession. In order to determine the maximum value, the maximum sum of the differential vector from the ideal signal status to the signal statuses, which have been produced (error vector), is sought in each decision field. In addition to the maximum value of the intermediate results, the maximum value of the modulation error ratio MERMAX is then calculated in accordance with the equation       MER    MAX    =            ·      100        ⁢                  Max        ⁢                  {                                                error              ⁢                                                          ⁢              vector                                            }                            VM        _              ⁢                  ⁢          (      %      )      
In this case {overscore (VM)} is the square weighted mean value of the amplitude of all ideal signal statuses of a carrier modulated with user data of the modulation type used in each case, which value is known or can be easily calculated for the modulation types used most frequently, such as 16 QAM, etc., and is used constant in the calculation.
All sums of the differential vectors from the ideal status to the status which has been produced are square and added to obtain the mean modulation error ratio and the number of symbols is counted. Subsequently, the mean modulation error ratio MERRMS is calculated in accordance with the equation       MER    RMS    =            100      ·                                                  1              n                                ⁢                                    ∑              n                        ⁢                                                                            error                  ⁢                                                                          ⁢                  vector                                                            2                                                VM          _                      ⁢                  ⁢          (      %      )      
Both of the values calculated in percent in accordance with the above equations can also be given in the logarithmic scale in dB in accordance with the following conversion:       MER    dB    =                    -        20            ·      1        ⁢                  ⁢    g    ⁢                  ⁢          (                        MER          ⁡                      (            %            )                          100            )        ⁢                  ⁢                  (        dB        )            .      
The term modulation error ratio and the corresponding laws of calculation for it have been established and standardized by the DVB Measurement Group in the ETR 290 for DVB-C and DVB-S. FIG. 1 shows by way of example the vectors required to calculate the modulation error ratio in the first quadrants and this is for 64 QAM.
It is known to calculate the modulation error ratio for a single carrier in each case in accordance with the above formula and to display it as a numerical value. For multicarrier systems with 1000 or even more individual carriers, as is the case in DAB with 1536 carriers and in DVB with 1705 or 6817 carriers even, this type of modulation error ratio calculation and individual carriers illustration is no longer useful.